The present invention relates to a coordinate positioning machine, such as a robot or a coordinate measuring machine used to measure the position, form, or dimension of components, for example.
One well known type of coordinate positioning machine has a xe2x80x9cCartesianxe2x80x9d configuration, in which an operating module (which may incorporate a probe, for example) is supported for movement relative to a base (such as a table) with three translational degrees of freedom by means of three xe2x80x9cseriallyxe2x80x9d mounted (i.e. one on top of another), mutually orthogonal linear guideways. In an alternative support configuration, an operating module is supported for movement relative to a table with three translational degrees of freedom by three articulating linkages, each of which is connected directly between the operating module and a support member which forms part of the base. Such a xe2x80x9cparallelxe2x80x9d mounting configuration for a machine is known from EP 102744 and U.S. Pat. No. 4,976,582, for example.
Various aspects of the present invention relate to the provision of a machine configuration of the parallel type.
A first aspect of the present invention provides a coordinate positioning machine having a base and an operating module interconnected by three linkages which cooperate to prevent relative rotation of the base and the operating module, but permit relative translational motion of the base and the operating module, the machine further comprising selectively operable locking means which constrains the operating module to move in a locked plane relative to the base.
One of the advantages of such a machine configuration is that it provides the user with the ability to operate such a machine manually to scan the profile of an object in a series of parallel planes for the purpose, for example, of obtaining a data map of its surface. Preferably the machine includes a pair of selectively operable locking means which are actuable to constrain relative motion of the base and operating module in non-parallel planes, the displacement of which within the working area of the machine is determined on the basis of the position of the operating module at the instant when the locking means are actuated to constrain the relative motion.
Accordingly, one preferred embodiment of the machine includes: first and second selectively operable locking means, wherein locked planes in which relative motion of the operating module and base is constrained by the first locking means are non-parallel to locked planes in which relative motion is constrained by the second locking means.
In a further preferred embodiment of the machine the position of a locked plane in which the operating module is constrained to move by the selectively operable locking means is selectable by the user of the machine on the basis of an instantaneous position of the operating module at an instant when the selectively operable locking means is actuated to constrain motion of the operating module.
Preferably at least one of the linkages has first and second limbs which are pivotally interconnected with two degrees of rotational freedom, the first limb comprising a pair of elongate struts which are pivotally mounted with two degrees of rotational freedom at one end to one of the base and operating module, and at the other end to the second limb, and the second limb is pivotally mounted to the other of the base and the operating module with one degree of freedom about an axis of articulation, wherein the selectively operable locking means operates between the struts of the first limb.
A preferred feature of such an embodiment provides that each of the locking means comprises an elongate clamp connected at each of its ends to one of the struts, wherein when the clamp is not operating, its length increases and decreases with pivoting of the limbs, and when the clamp is operating it is operable to maintain its length at a constant value.
In an independent aspect of the present invention, relative displacement of the base and the operating module in a machine of the parallel type is determined by means of a plurality of encoders. According to this aspect of the present invention, there is provided a coordinate positioning machine having a base and an operating module interconnected by three linkages which cooperate to prevent relative rotation of the base and the operating module, but permit relative translational motion of the base and the operating module, each of the linkages having first and second limbs pivotally interconnected with two degrees of rotational freedom, the first limb being pivotally mounted at one end with two rotational degrees of freedom to one of the base and the operating module, and at the other end to the second limb, and the second limb being pivotally mounted to the other of the base and operating module with one degree of freedom about an axis of articulation, wherein relative displacement of the operating module and base is determined by means of three or more encoders, each encoder having:
a scale which is mounted to an arcuate substrate and is defined by a series of spaced-apart lines;
a readhead mounted in register with the scale, the scale and the readhead being relatively moveable in a direction of spacing of the lines;
the substrate being mounted to one of: the base, the operating module, and a limb of the linkage;
the readhead being mounted to a part of the machine on which the scale substrate is not mounted, such that the readhead and scale substrate are pivotable relative to one another about an axis substantially coincident with the geometric centre of the arcuate scale substrate.
Preferably the readhead is mounted to the base, and the arcuate substrate is mounted to the second limb, wherein the geometric centre of the arcuate substrate lies substantially coincident with the axis of articulation.
In a further preferred embodiment, the base includes a table which, in use, supports an object which is to be operated upon by the machine, and a pillar extending upwardly from the base, wherein the linkages extend transversely from the pillar to the operating module, so that during motion of the operating module toward and away from the pillar, the operating module traverses the table, wherein the readhead is mounted to the pillar and the second limb is mounted at one end to the pillar.
The encoders may be opto-electronic, magnetic or capacitive, for example.
Desirably, the base and operating module have a mechanical reference position at which their relative displacement is repeatable. This enables the encoders, and any associated error map, to be initialised at the same mechanical position each time. Preferably the mechanical reference position will also serve as a detent mechanism by means of which the operating module may be retained in a xe2x80x9cparkedxe2x80x9d position relative to the base when the machine is not in use.
Preferably, the machine will also have a configuration which prevents unwanted relative motion of the base and operating module. Accordingly, a further independent aspect of the present invention provides a coordinate positioning machine having a base and an operating module interconnected by three linkages which cooperate to prevent relative rotation of the base and the operating module, but permit relative linear motion of the base and the operating module, wherein the effect of gravitational force on the operating module is counteracted by one or more counterbalancing devices which act to suspend the operating module relative to the base when no external forces act on the operating module.
The nature of the operating module is dependant upon the nature of the tasks the user of the machine may wish to perform. For example, as mentioned above, the operating module may include either a trigger or a measuring probe (which may be either a contact or a non-contact probe), a cutting tool, or a welding arm, gripper or paint spraying nozzle, for example. The operating module may also include an articulating head for orienting such a probe (for example) with one or more degrees of rotational freedom relative to the base.